Just a stab in the dark, but you’ve probably heard: There is a total solar eclipse today, August 21.

For the first time since 1979, the moon’s shadow will zip across the continental United States. The shadow will travel from Oregon to South Carolina in a swift 92 minutes. For those in the path of totality, total darkness will last only a couple of minutes. There and elsewhere in most of the United States, the moon will partially block the sun for around three hours.
If you don’t already have plans to travel to the 115-kilometer-or-so-wide path of totality, well, you’re probably too late. But here are some links to help you experience the eclipse, whether or not you’re able to see it in person.

The eclipse will be visible in all of North America — as well as in Central America and a small part of South America. Wondering what you’ll see where you live? Check out this interactive map from NASA or this cool tool from Vox.

Still need eclipse glasses? While many retailers have been sold out for days, some organizations are handing out free glasses at eclipse-watching events. Check your local TV/newspaper/radio stations’ newsfeeds for the latest. Make sure your glasses are safe.

No eclipse glasses? Never fear! You can still see the moon eclipsing the sun by making a pinhole projector or a box projector. Or just let sunlight shine through something that has holes, like a colander or Ritz Cracker (look at the ground to see the shape of the shadow the holes cast).

Watching with kids? Check out Growth Curve blogger Laura Sanders’ tips for protecting little ones’ eyes during the eclipse.
Which reminds me: Whatever you do, don’t look directly at the sun. Permanent damage to your eyes may result. If you’re in the path of totality, officials say it’s OK to look directly at the sun once the moon completely blocks it. But that’s very brief, so be prepared to quickly look away or shield your eyes once the moon slips out of total alignment.

Want to do more with your eclipse experience? It’s not too late to participate in a citizen science project.

Stuck indoors, or out of totality? Watch the livestream. NASA’s programming begins at noon Eastern on NASA TV, which you can watch at this link or right here:
Want some tunes to go along with it? The NASA interns made an eclipse playlist. There are also several Spotify playlists around, like this one from WXPN, this from the Washington Post and this one from the Boston Globe.

If all this excitement has you fancying a future in eclipse chasing, check out our interactive map of the next 15 total solar eclipses.

And let’s not forget that there will be a ton of science going on during the eclipse. Here are the big questions physicists and astronomers will seek to answer today.

Still want more? Follow us on Facebook and on Twitter for eclipse updates and RT’s of our correspondents in totality. Watch as the Science News team takes over the Society for Science & the Public’s Snapchat (Society4Science). And come back to Science News later today for a report from our astronomy writer, Lisa Grossman, who is spending the day in Casper, Wyo., with a research team that’s studying the sun’s wispy atmosphere, the corona.

Molecules are seriously chilling out. Scientists report the first cooling of molecules below a previously impassable milestone. The result, in which scientists cooled molecules down to tens of millionths of a degree, is a step toward reaching the ultracold temperatures already achievable with atoms, researchers report August 28 in Nature Physics.

Scientists regularly chill atoms to less than a millionth of a degree above absolute zero (‒273.15° Celsius), even reaching temperatures as low as 50 trillionths of a degree (SN: 5/16/15, p. 4). But molecules are more difficult to cool down, as they can spin and vibrate in a variety of ways, and that motion is a form of heat.
Previously, physicists have made ultracold molecules by convincing prechilled atoms to link up (SN: 12/20/08, p. 22), but the technique works for only a few kinds of molecules. Putting the freeze on already assembled molecules has allowed scientists to chill additional types but, until now, down to only a few hundreds of millionths of degrees.

Using lasers and magnetic fields, the scientists corralled and cooled molecules inside a device called a magneto-optical trap. In the trap, molecules of calcium monofluoride are slowed — and therefore cooled — when they absorb photons from a laser. But only so much cooling is possible with this method. To go beyond what’s called the Doppler limit, the researchers adapted a method used for cooling atoms, known as Sisyphus cooling. Two lasers pointed at one another create an electromagnetic field that acts like an endless hill the molecule must climb, thereby sapping its energy and heat. With these two techniques, the molecules reached a frigid 50 millionths of a degree above absolute zero.
As the art of laser cooling advanced in recent decades, ultracold atoms rapidly became a popular research topic. Now, predicts study coauthor Michael Tarbutt, a physicist at Imperial College London, cold molecule research is “going to explode in exactly the same way that it did for cold atoms.”
Cold molecules could be useful for a variety of scientific purposes: studying how chemical reactions occur, looking for hints of new fundamental particles or simulating complex quantum materials in which many particles interact at once.

“It’s a really exciting result,” says physicist David DeMille of Yale University, who was not involved with the research. “It turns out it’s harder in almost every way to apply laser cooling and trapping to molecules, but there are many, many motivations for doing that.”

Immune cells can turn certain invaders on themselves, forcing them to prematurely self-destruct, researchers have discovered.

In mice, when white blood cells in the lungs engulf spores of a common airborne fungus, these immune cells release an enzyme that sends the fungal cells into programmed cell death. That prevents the spores from setting up shop in the lungs and sparking a potentially deadly lung infection, the researchers report in the Sept. 8 Science.

Found naturally in soil and decaying organic matter, the fungus, Aspergillus fumigatus, releases airborne spores that are found in small doses in the air people breathe every day. The finding may help explain why most people can regularly inhale the spores and not get sick. In people with weakened immune systems, though, this natural defense system doesn’t work. This research could eventually lead to better treatments for these patients.
Programmed cell death is a natural part of a cell’s life cycle — a way for organisms to break down old cells and make way for new ones. “Research in the last couple of decades has shown that microbes can exploit [cell death] pathways to cause disease,” says study coauthor Tobias Hohl, an infectious disease researcher at Memorial Sloan Kettering Cancer Center in New York City. But this study shows that the tables can be turned. “Not only can microbes exploit this in hosts, but host cells can exploit these pathways to instruct certain microbes to kill themselves.”

“The idea that the host triggers the mechanism of [programmed cell death] as a way of defending against infection is very cool,” says Borna Mehrad, a pulmonologist at the University of Florida College of Medicine in Gainesville who wasn’t part of the study.

Hohl and colleagues identified a gene in A. fumigatus that puts the brakes on programmed cell death. The gene, AfBIR1, shares an ancestor with the human gene survivin, which also regulates cell death.

When the researchers amped up the activity of AfBIR1 in a strain of the fungus, half the mice infected with the spores died during the eight-day study period. (Mice infected with unmodified spores were fine.) Cues that would normally send fungal cells to their death didn’t register, so the fungus was able to grow in the mice’s lungs.

In another experiment, the scientists gave mice a drug called S12, which took away AfBIR1’s brake effect. As a result, the mice were able to fight off the infection. “Those two findings suggested to us that this fungal [cell death] pathway really is critical,” Hohl says.
Hohl did this research with a special variety of A. fumigatus that changes color when its suicide instructions kick in. That advance allowed the researchers to make observations that weren’t possible before, Mehrad says.

For instance, Hohl and his colleagues noticed that fungal cells being engulfed by neutrophils, a type of white blood cell, appeared to be undergoing programmed cell death. That suggested that neutrophil activity might set off fungal programmed cell death.

Neutrophils release an enzyme called NADPH oxidase, and mice deficient in the enzyme weren’t as good at fending off the fungus, Hohl found. That makes sense with clinical data in humans too. People with a genetic mutation that causes a deficiency in NADPH oxidase are particularly at risk for developing an Aspergillus infection, Hohl says. People who have fewer neutrophils, due to chemotherapy or HIV infection, for instance, also make less of the enzyme and are less able to resist a fungal infection.

Survival rates vary, but the U.S. Centers for Disease Control and Prevention estimates that 41 percent of organ transplant recipients who contract aspergillosis die within a year. Seventy-five percent of stem cell transplant recipients with the infection die in that same time frame. Someday, a version of S12 that’s modified to work in humans might be able to boost these patients’ defenses against A. fumigatus infections, Hohl suggests.

In the future, he wants to see whether the same mechanisms extend to other fungal species too.

Finding a great glue is a sticky task — especially if you want it to attach to something as slick as the inside of the human body. Even the strongest human-made adhesives don’t work well on wet surfaces like tissues and organs. For surgeons closing internal incisions, that’s more than an annoyance. The right glue could hold wounds together as effectively as stitches and staples with less damage to the surrounding soft tissue, enabling safer surgical procedures.

A solution might be found under wet leaves on a forest floor, recent research suggests. Jianyu Li of McGill University in Montreal and colleagues have created a surgical glue that mimics the chemical recipe of goopy slime that slugs exude when they’re startled. The adhesive stuck to a pig heart even when the surface was coated in blood, the team reported in the July 28 Science. Using the glue to plug a hole in the pig heart worked so well that the heart still held in liquid after being inflated and deflated tens of thousands of times. Li, who did the research while at Harvard University, and colleagues also tested the glue in live rats with liver lacerations. It stopped the rats’ bleeding, and the animals didn’t appear to suffer any bad reaction from the adhesive.
The glue has “excellent, excellent properties,” says Andrew Smith, a biologist at Ithaca College in New York.
And slugs aren’t the only biological inspiration for new adhesives. Clues to better glues have long been hiding out in damp, soggy and downright wet places. For slugs, mussels, marine worms and a cadre of other critters, secreting sticky substances that attach strongly to soaked surfaces is just a fact of life. That’s why scientists are studying the structures of those substances to design new and better surgical adhesives.

“There’s really a big need to develop new ways of sealing tissues, of affixing devices to tissues — in particular, for minimally invasive procedures,” says Jeff Karp, a biomedical engineer at Brigham and Women’s Hospital in Boston. While existing medical-grade superglue is great at sealing up fingertip cuts, it is too toxic to use inside the body. Other alternatives just aren’t sticky enough to fully replace stitches. With a better glue, surgeons could also make snips that are too tiny to be stitched or stapled closed. Smaller incisions speed healing time and decrease risk of complications, Karp says.

Smith says he isn’t surprised that slug slime could lead to a big advance. For several years, he’s been trying to understand how the slug Arion subfuscus builds its ooze. For his research, Smith prods slugs gently with the tip of a metal spatula to startle them, and scoops up the slime as it’s released. “If you get it on your hands, it’ll set within seconds into an extremely sticky material,” he says.
The goo, Smith and others have found, overcomes a major challenge that adhesive designers face. It seems obvious that glue should be sticky. Yet the molecules in glue need to adhere not just to the things you’re trying to stick together, but also to each other. And that stickiness can’t come at the expense of flexibility, especially for medical applications. Soft, squishy organs are going to jiggle; skin is going to stretch. Without some bendiness, the glue might attach securely to each of the surfaces being stuck together, but the glob of glue itself might snap or shear under stress.

Slug defense slime solves that problem with two interwoven networks of molecules, tangled together like strings of holiday lights. One network is rigid, with chemical bonds that break easily, Smith says. The other is deformable, stretching substantially without breaking. This combo makes the goo simultaneously tough, flexible and sticky.

Li’s slug-inspired adhesive takes a similar approach. One layer of the material is a polymer, a type of material made from long molecules built from many repeated subunits, like a string of beads. Positively charged appendages dangling off the polymers are drawn to wet tissue surfaces by the same forces underlying static electricity. This first layer weaves into another layer, a water-based gel. The gel layer acts like a shock absorber in a car, Li says. It soaks up energy that might otherwise dislodge or snap the adhesive.

Despite being 90 percent water, the material is both sticky and tough, Li says. The fact that it’s mostly water makes it more likely to be nontoxic to humans.
Though Li’s adhesive has been tested only in human cell cultures and in lab animals, another bio-inspired glue has made its way into human trials. It’s based on work published by Karp and colleagues in 2014 in Science Translational Medicine. Karp’s team developed a viscous liquid that solidifies into a tough but stretchy glue when illuminated by light, and demonstrated that the liquid can seal holes in hearts.

“Nothing we create is really that similar to anything you see in nature, but some of the ideas gave us critical insights,” Karp says. The researchers realized, for example, that a lot of natural glues that work in water have hydrophobic elements that help clear away the water for a better stick. The research sparked Karp and colleagues to found a company, Gecko Biomedical, which Karp now advises. On September 11, the company announced the completion of a small clinical trial of its adhesive: The sealant immediately stopped blood flow after an artery-clearing operation in about 85 percent of 22 participants. Because of that success, Gecko Biomedical now has approval to market the glue in Europe.

Bio-inspired adhesives can do more than patch up incisions, though. Russell Stewart, a bioengineer at the University of Utah in Salt Lake City, is tapping into marine-dwelling sandcastle worms for a different glue goal: He wants to create a better embolic agent — a way to deliberately block blood flow to certain tissues. Embolic agents can cut blood flow to a tumor, say, or stem internal bleeding. Often, these materials are liquids that reach their target through a catheter and then solidify into a sticky mass to block tiny vessels. But such glues can be difficult to control — they need to harden at just the right time and current options often rely on harsh materials that require special equipment and can cause pain for patients.

Inspired by the sandcastle worm (Phragmatopoma californica), Stewart has designed a new — and he thinks better — embolic agent. A sandcastle worm uses fingerlike appendages coming out of its face to arrange grains of sand into expansive tubular reefs. It squirts small dabs of a liquid adhesive out of these appendages to make the grains stick together. That glue’s structure is quite different from slug slime, Stewart has found. It’s a solution of oppositely charged proteins strongly attracted to each other. The proteins make up a dense liquid that doesn’t mix with water. A worm packages each ingredient in the glue separately, so the proteins combine only once secreted. After mixing, the glue solidifies in about 30 seconds.

Stewart’s mimic also starts out as a liquid that transforms into a hard foamlike material within a few seconds of hitting blood, his team reported in 2016 in Advanced Healthcare Materials. That means the material can be injected as a liquid and doesn’t harden until it’s in the right place. Early tests have been promising: The foam completely blocked the arteries of rabbits’ kidneys without moving into tissue where it didn’t belong.

The range of biological adhesives is impressive, says Jonathan Wilker, a chemist at Purdue University in West LaFayette, Ind. “They’re so wildly different,” both in terms of chemical makeup and functional properties. That diversity provides a wide palette for scientists seeking glues for specialized applications. And Wilker’s own work adds mussels to the list.

Mussels secrete a strong adhesive that helps them stick tenaciously to rocks and ship hulls. Their secret is a molecule called DOPA, Wilker says. DOPA, or 3,4-dihydroxyphenylalanine, sticks well to other DOPA molecules and to other substances. That gives it the same balance of toughness and stickiness that’s also found in slug slime. Certain amino acids found in mussel proteins might also aid the underwater adhesion. For example, an amino acid called lysine that hangs off of mussel adhesion proteins appears to help clear water molecules out of the way, leaving a drier surface for proteins glomming on.
Wilker’s copycat adhesive is made up of long chains of polystyrene molecules (essentially, Styrofoam) with units of DOPA mixed in. Those long chains of tricked-out polystyrene molecules tangle together and cross-link to create a strong adhesive. He’s made different varieties of the mimic, tailored for different applications. After being immersed in water, one version held on tighter underwater than the glue made by mussels themselves, Wilker’s team reported in February in Applied Materials Interfaces. Another version is biodegradable.

If he can make the glues nontoxic to cells, they could possibly be used inside the body. In one recent study, Wilker created an artificial adhesive protein that mimics the natural protein elastin. The artificial version excelled in both dry and damp test environments, his team reported in April in Biomaterials.

Bringing animal-inspired adhesives into the human body won’t necessarily be a simple task, though. It requires tackling some problems that other animals don’t need to solve, Karp says. A slug, for instance, produces its slime as it needs it. It doesn’t stockpile gallons of glue in its tiny body, or instantly churn out a year’s supply. A successful real-world glue, however, will need to be easy to produce in large quantities and safe to store for months at a time, Karp points out. Those are problems humans will have to solve on their own. That’s the next challenge.

Subtle cosmic vibrations kicked up by swirling black holes have captured the public imagination — and the minds of the physics Nobel Prize committee members, too.

Three scientists who laid the groundwork for the first direct detection of gravitational waves have won the Nobel Prize in physics. Rainer Weiss of MIT, and Kip Thorne and Barry Barish, both of Caltech, will share the 9-million-Swedish-kronor (about $1.1 million) prize, with half going to Weiss and the remainder split between Thorne and Barish.
Though researchers often wait decades for Nobel recognition, the observation of gravitational waves was so monumental that the scientists were honored less than two years after the discovery’s announcement.

“These detections were so compelling and earth shattering…. Why wait?” says Clifford Will of the University of Florida in Gainesville, who was not directly involved with the discovery. “It’s fabulous. Absolutely fabulous.”

Weiss, Thorne and Barish are pioneers of the Laser Interferometer Gravitational Wave Observatory, or LIGO. On February 11, 2016, LIGO scientists announced they had spotted gravitational waves produced by a pair of merging black holes. This first-ever detection generated a frenzy of excitement among physicists and garnered front-page headlines around the world.

LIGO’s observation of gravitational waves directly confirmed a 100-year-old prediction of Einstein’s general theory of relativity — that rapidly accelerating massive objects stretch and squeeze spacetime, producing ripples that travel outward from the source (SN: 3/5/16, p. 22).
“If Einstein was still alive, it would be absolutely wonderful to go to him and tell him about the discovery. He would be very pleased, I’m sure of it,” Weiss said during a news conference at MIT a few hours after he got word of the win. “But then to tell him what the discovery was, that it was a black hole, he would have been absolutely flabbergasted because he didn’t believe in them.”

As enthusiastic team members clad in LIGO-themed T-shirts celebrated the discovery, Weiss stressed that the discovery was a group effort. “I’m a symbol of that. It’s not all on my shoulders, this thing,” he said, citing the large collaboration of scientists whose work led up to LIGO’s detection.

Physicists anticipate that LIGO will spark an entirely new field of astronomy, in which scientists survey the universe by feeling for its tremors. “It will allow us to see the parts of the universe that were not revealed to us before,” says LIGO team member Carlos Lousto of the Rochester Institute of Technology in New York.

LIGO’s first incarnation, which officially began collecting data in 2002 and ran intermittently until 2010, yielded no hints of gravitational waves. After years of upgrades, the souped-up detectors, known as Advanced LIGO, began searching for spacetime ripples in 2015. Almost as soon as the detectors were turned on — even before scientific data-taking had formally begun — scientists detected the minuscule undulations of their first black hole collision. Those ripples, spotted on September 14, 2015, journeyed to Earth from 1.3 billion light-years away, where they were produced by two colossal black holes that spiraled inward and merged into one (SN: 3/5/16, p. 6).

Quivers from those converging black holes, when converted into an audio signal, made a tell-tale sound called a “chirp,” reminiscent of a bird’s cry. The particulars of that signature reveal details of the collision. “The beauty of the symphony is in what you can extract from the tiny wiggles, or the wiggles on tops of wiggles, in that signal,” Thorne said at an Oct. 3 news conference at Caltech.
Since that first detection, scientists have observed three more black hole collisions. And additional gravitational ripples may already be in the bag: It’s rumored that LIGO scientists have also detected a smashup of neutron stars (SN Online: 8/25/17). In fact, Weiss teased an announcement to come on October 16.

An astounding feat of engineering, LIGO consists of two enormous L-shaped detectors that stretch across the wooded landscape of Livingston, La., and the desert of Hanford, Wash. Each detector boasts two 4-kilometer-long arms through which laser light bounces back and forth between mirrors.

Gravitational waves passing through a detector stretch one arm while shortening the other. LIGO compares the arms’ sizes using the laser light to measure length differences a tiny fraction of the size of a proton. Gravitational waves should produce signals in the two distant detectors nearly simultaneously, helping scientists to rule out spurious signals that can be caused by events as mundane as a truck bouncing along nearby.

“LIGO is probably one of the best and most amazing instruments ever built by mankind,” Barish said at the Caltech news conference. But building it was a risky endeavor: No one had previously attempted anything like it, and no one could say for sure whether the effort would succeed. “What’s fundamental is you have to be willing to take risks to do great things,” Barish said.

In August, LIGO’s two detectors teamed up with the similarly designed Virgo detector near Pisa, Italy (SN Online: 8/1/17). The latest gravitational wave sighting, made on August 14, showed up in all three detectors almost simultaneously, which allowed scientists to pinpoint the region of space in which the black holes resided more precisely than ever before (SN Online: 9/27/17).

Weiss spent decades on the project, beginning with nascent scribbles on scraps of paper and early prototypes. In the 1960s, Weiss came up with the idea for a laser gravitational wave detector while teaching a class on general relativity. (Other researchers had independently proposed the technique as well.) He refined that idea and built a small, prototype detector, establishing the basic blueprint that would eventually evolve into LIGO.
Inspired by a conversation with Weiss, Thorne, who had been studying theoretical aspects of gravitational waves, assembled a team to work on the technique at Caltech in the ’70s. (Thorne was a 1958 semifinalist in the Science Talent Search, a program of the Society for Science & the Public, which publishes Science News.)

Another LIGO founder, Ronald Drever, died in March. Drever, who had been working on gravitational wave detectors at the University of Glasgow, joined Thorne at Caltech in 1979. Weiss and Drever each worked individually on prototypes, before Weiss officially teamed up with Thorne and Drever in 1984 to create LIGO (SN: 3/5/16, p. 24). Drever did live to hear of the first detection, Will says, but “it’s sad that he didn’t live to see it all.”

Barish joined the project later, becoming director of LIGO in 1994. He stayed in that role for more than 10 years, elevating LIGO from scientists’ daydreams into reality. Barish oversaw construction and commissioning of the detectors, as well as initial gravitational wave searches. “He entered the experiment in a crucial moment, when it was necessary to bring the experiment to a different level, make it a big collaboration,” says Alessandra Buonanno of the Max Planck Institute for Gravitational Physics in Potsdam, Germany.

Speculation that LIGO would nab a Nobel began as soon as the discovery was announced. So the collaboration was not surprised by the honor. “We were certainly expecting this to happen,” says LIGO team member Manuela Campanelli of the Rochester Institute of Technology. Still, the lack of surprise didn’t dampen the mood of festivity. “I feel in a dream,” says Buonanno.

LIGO and Virgo are currently in a shutdown period while scientists tinker with the detectors to improve their sensitivity. The gravitational wave hunt will resume next year. Besides black hole mergers and neutron star smashups, in the future, scientists might also spot waves from an exploding star, known as a supernova. Upcoming detectors might sense trembles generated in the Big Bang, providing a glimpse of the universe’s beginnings.

And scientists may even find new phenomena that they haven’t predicted. “I await expectantly some huge surprises in the coming years,” Thorne said.

SEATTLE — Earth weakened by previous landslides and soils behaving like water were responsible for the unusual size of a deadly 2014 landslide, two scientists reported October 24 at the Geological Society of America’s annual meeting. Understanding why this landslide was so mobile could help geologists better map the hazards that could lead to others like it and prevent future loss of life.

In March 2014, following more than a month of heavy rainfall, a wall of mud suddenly rushed down a hillside near Oso, Wash., engulfing houses and trees before spilling into the Stillaguamish River valley (SN: 4/19/14, p. 32). The debris flow killed 43 people and destroyed dozens of homes. The valley had seen landslides before, most recently in 2006. But the “run-out” — the size of the debris flow — of the Oso landslide was uncommonly large, spreading a fan of mud and debris across 1.4 kilometers.

To unravel the sequence of events leading to the landslide, Brian Collins and Mark Reid, both with the U.S. Geological Survey in Menlo Park, Calif., first mapped the debris that made up the landslide, including large still-intact blocks of hillside called hummocks, glacial sediments and fallen trees. The researchers then used those maps to track where the different parts of the debris had originated and where they ended up. From that, the duo determined that sediments weakened and previously mobilized by the 2006 landslide failed first, followed by sediments that had failed in a prehistoric landslide and finally by intact sediments.

Once it began to flow, the landslide didn’t sweep smoothly down the hill, the researchers determined. Instead, segments collided into one another and then stretched apart — extending and contracting earthwormlike — as more and more of the slope fell and transferred its momentum to the landslide. The sudden piling-on of mass also caused the soils beneath the hummocks and larger debris to weaken and become “liquefied,” or behave like water. And those liquefied soils then helped raft the hummocks and trees much farther out into the valley.

Some bridges could really put a swing in your step.

Crowds walking on a bridge can cause it to sway — sometimes dangerously. Using improved simulations to represent how people walk, scientists have now devised a better way to calculate under what conditions this swaying may arise, researchers report November 10 online in Science Advances.

When a bridge — typically a suspension bridge — is loaded with strolling pedestrians, their gaits can sync, causing the structure to shimmy from side to side. The new study “allows us to better predict the crowd size at which significant wobbling can appear abruptly,” says mathematician Igor Belykh of Georgia State University in Atlanta.
Engineers might eventually use the researchers’ results to avoid debacles like the one that befell the Millennium Bridge in London. This suspension bridge temporarily shut down just days after it opened in 2000 due to the large wobble that occurred when many people tromped across it at once (SN: 11/24/07, p. 331), necessitating costly repairs to fix the problem.

Pedestrians crossing a bridge can cause slight sideways motion of the bridge as they push with their feet. This swaying may lead to the crowd unintentionally falling into lockstep because it’s easier to go with the flow of the swinging bridge than fight it. That synchronization, in turn, creates larger and larger oscillations.
“It’s a dangerous phenomenon that could cause a bridge to collapse if it went unchecked,” says applied mathematician Daniel Abrams of Northwestern University in Evanston, Ill., who was not involved with the research.

Previous mathematical models of the phenomenon “didn’t realistically capture how people exerted force on the bridge,” Abrams says, “but this new model is pretty realistic.” Whereas earlier simulations focused on the timing of footfalls or the amount of force produced with each step, the new work takes both into account.

Tests of the Millennium Bridge showed that the lurching occurred only after a critical number of people — around 165 — entered the bridge. Likewise, in their simulations, Belykh and his colleagues find that oscillations begin abruptly above a certain threshold number of walkers, depending on the properties of the bridge.

The research challenges some previous assumptions. For instance, in the new simulations, the onset of the wobbling began just before the walkers joined in lockstep. This suggests that the synchrony of the crowd might not be a root cause but instead acts as a feedback effect that amplifies preexisting small-scale wobbles. That insight could be relevant for wobbles that occur in certain bridges without pedestrians syncing, Belykh says. Future work will further investigate how the swaying starts.

Cholera strains behind worldwide outbreaks of the deadly disease over the last five decades are jet-setters rather than homebodies.

It had been proposed that these cholera epidemics were homegrown, driven by local strains of Vibrio cholerae living in aquatic ecosystems. But DNA fingerprints of the V. cholerae strains behind recent large outbreaks in Africa and Latin America were more closely related to South Asian strains than local ones, according to two papers published in the Nov. 10 Science.
This evidence that the guilty strains traveled from abroad could guide public health efforts, the researchers say. “If you don’t understand how the bug spreads, then it’s very difficult to try to stop the bug,” says François-Xavier Weill, a clinical microbiologist at the Institut Pasteur in Paris who coauthored both papers.

People are exposed to V. cholerae by consuming water or food contaminated by the bacteria. Poor sanitation and drinking water treatment can fuel an epidemic, as seen in Yemen (SN: 8/19/17, p. 4), where nearly a million people are suspected to have been infected and more than 2,000 have died in the world’s largest recorded cholera outbreak.

A cholera infection can produce mild or no symptoms. But about one in 10 people will rapidly develop severe diarrhea and dehydration that, without treatment, can kill within hours. Although underreported, cholera cases worldwide each year are estimated to range from 1.4 million to four million, and 21,000 to 143,000 people die from the disease, according to the World Health Organization’s Global Health Observatory.
There have been seven cholera pandemics, or global outbreaks, since the 19th century, when the bacteria spread from its original home on the Indian subcontinent. The seventh one, which began in Indonesia in 1961, reached Africa in 1970 and hit Latin America in 1991, is still ongoing. It’s attributed to strains that originated near the Bay of Bengal, where cholera is a seasonal occurrence.

But it was unclear whether the large outbreaks happening around the world were related to each other, or if they had each originated from local strains. Previous methods used to track V. cholerae were unable to distinguish strains with enough detail, Weill says. “It was impossible then, during the last 50 years, to understand the routes of propagation of cholera.”

Weill and an international research team analyzed the genetic information of about 1,700 strains of V. cholera, including those collected during and in between outbreaks over about 40 years from 45 countries in Africa and 14 countries throughout Latin America.

In both Africa and Latin America, the strains responsible for the large epidemics were most closely related to the South Asian strains, rather than strains existing in the local environment. These “epidemic” strains have been introduced 11 times in Africa since 1970 and have caused large outbreaks that lasted as long as 28 years, the researchers found.

In Latin America, there were three main introductions of the South Asian “epidemic” strains. One that came through Africa hit Peru in 1991. Another invaded Mexico around the same time, possibly arriving with coca smugglers using an airstrip near Mexico City. The third introduction, from Nepalese United Nations personnel, devastated Haiti in 2010 (SN: 2/25/12, p. 16).

“We now know what cholera is with much more precision,” says Nicholas Thomson, a genome scientist at the Wellcome Trust Sanger Institute in Cambridge, England, who also coauthored both papers. “You can find V. cholerae in the environment, no doubt about it, but the patterns of spread tell you that that’s not the primary route of transmission.” Rather, he says, it’s transmission between people that allows the bacteria to spread rapidly internationally.

“These studies affirm the primary role that people play in the spread of cholera,” says Yonatan Grad, an infectious diseases clinician at Harvard T.H. Chan School of Public Health in Boston who was not involved with the studies. “The emphasis on infected people as the vectors for spread underscores the importance of vaccination as a strategy to limit cholera.”

Some scientific anniversaries celebrate events so momentous that they capture the attention of many nonscientists as well — or even the entire world.

One such anniversary is upon us. December 2 marks the semisesquicentennial (75th anniversary) of the first controlled and sustained nuclear fission chain reaction. Only four years after German scientists discovered nuclear fission, scientists in America took the first step toward harnessing it. Many of those scientists were not Americans, though, but immigrants appalled by Hitler and horrified at the prospect that he might acquire a nuclear fission weapon.

Among the immigrants who initiated the American fission effort was Albert Einstein. His letter to President Franklin Roosevelt, composed at the request and with the aid of immigrant Leo Szilard from Hungary, warned of nuclear fission’s explosive potential. Presented with Einstein’s letter in October 1939, Roosevelt launched what soon became the Manhattan Project, which eventually produced the atomic bomb. It was another immigrant, Enrico Fermi from Italy, who led the initial efforts to show that building an atomic bomb was possible.

Fermi had arrived in the United States in January 1939, shortly after receiving the Nobel Prize in physics for his work on creating artificial elements heavier than uranium. Except that he hadn’t actually done so — his “new elements” were actually familiar elements produced by the splitting of the uranium nucleus. But nobody knew that fission was possible, so Fermi had misinterpreted his results. Chemists Otto Hahn and Fritz Strassmann, working in Germany, conducted experiments in 1938 that produced the element barium by bombarding uranium with neutrons. So Hahn and Strassmann got the credit for discovering fission, although they didn’t really know what they had done either. It was Lise Meitner, a former collaborator of Hahn’s who had recently left Germany to avoid Nazi anti-Semitism, who figured out that they had split the uranium nucleus.
Meitner’s nephew Otto Frisch revealed her insight to Niels Bohr, the world’s leading atomic physicist, just as he stepped aboard a ship for a visit to America. Upon arriving in the United States, Bohr informed Fermi and Princeton University physicist John Archibald Wheeler of Hahn’s experiment and Meitner’s explanation. Fermi immediately began further experimental work at Columbia University to investigate fission, as did Szilard, also at Columbia (and others in Europe); Bohr and Wheeler tackled the issue from the theoretical side.

Fermi and Szilard quickly succeeded in showing that a fission “chain reaction” was in principle possible: Neutrons emitted from fissioning uranium nuclei could induce more fission. By September, Bohr and Wheeler had produced a thorough theoretical analysis, explaining the physics underlying the fission process and identifying which isotope of uranium fissioned most readily. It was clear that the initial speculations about fission’s potential power had not been exaggerated.

“Almost immediately it occurred to many people around the world that this could be used to make power and that it could be used for nuclear explosives,” another immigrant who worked on the Manhattan Project, the German physicist Hans Bethe, told me during an interview in 1997. “Lots of people verified that indeed when uranium is bombarded by neutrons, slow neutrons in particular, a process occurs which releases tremendous amounts of energy.”
Bethe, working at Cornell University, did not immediately join the fission project — he thought building a bomb would take too long to matter for World War II. “I thought this had nothing to do with the war,” he said. “So I instead went into radar.”

Fermi, despite being an immigrant, was put in charge of constructing an “atomic pile” (nowadays nuclear reactor) to verify the chain reaction theory. He was, after all, widely acknowledged as the world’s leading nuclear experimentalist (and was no slouch as a theorist either); colleagues referred to him as “The Pope” because of his supposed infallibility. Construction of the pile began on a squash court under the stands of the University of Chicago’s football stadium. The goal was to demonstrate the ability to generate a chain reaction, in which any one fissioning nucleus would emit enough neutrons to trigger even more nuclei to fission.

“It became clear to Fermi almost immediately that in order to do this with natural uranium you had to slow down the neutrons,” Bethe said.

Fermi decided that the best material for slowing neutrons was graphite, the form of carbon commonly used as pencil lead. But in preliminary tests the graphite did not do the job as Fermi had anticipated. He reasoned that the graphite contained too many impurities to work effectively. So Szilard began searching for a company that could produce ultrapure graphite. He found one, Bethe recalled, that happily agreed to meet Fermi’s purity requirements — for double the usual graphite price.
Ultimately Fermi’s atomic pile succeeded, producing a sustained chain reaction on December 2, 1942. That success led to the establishment of the secret laboratory in Los Alamos, N.M., where physicists built the bombs that brought World War II to an end in 1945.

By then, Bethe had been persuaded to join the project. He arrived at Los Alamos in April 1943 and witnessed the first nuclear explosion, at Alamogordo, N.M., on July 16, 1945.

“I was among the people who looked at it from a 20-mile distance,” he said. “It was impressive.”

Historians frequently cite the report of J. Robert Oppenheimer, director of the Los Alamos project, who said that the explosion reminded him of a line from the Hindu Bhagavad Gita: “Now I am become Death, the destroyer of worlds.”

Bethe recalled a different response, from one of the military officials on the scene.

“One of the officers at the explosion said, ‘My god. Those longhairs have let it get away from them.’”

Honeybees and bumblebees have a way to resist toxic compounds in some widely used insecticides.

These bees make enzymes that help the insects break down a type of neonicotinoid called thiacloprid, scientists report March 22 in Current Biology. Neonicotinoids have been linked to negative effects on bee health, such as difficulty reproducing in honeybees (SN: 7/26/16, p 16). But bees respond to different types of the insecticides in various ways. This finding could help scientists design versions of neonicotinoids that are less harmful to bees, the researchers say.
Such work could have broad ramifications, says study coauthor Chris Bass, an applied entomologist at the University of Exeter in England. “Bees are hugely important to the pollination of crops and wild flowers and biodiversity in general.”

Neonicotinoids are typically coated on seeds such as corn and sometimes sprayed on crops to protect the plants from insect pests. The chemicals are effective, but their use has been suspected to be involved in worrisome declines in numbers of wild pollinators (SN Online: 4/5/12).

Maj Rundlöf of Lund University in Sweden helped raise the alarm about the insecticides. In 2015, she reported that neonicotinoid-treated crops reduced the populations of bees that fed from the plants. Rundlöf, who was not involved with the new study, says the new research is important because it clarifies differences between the insecticides. “All neonicotinoids are not the same,” she says. “It’s a bit unrealistic to damn a whole group of pesticides.”

Bass and his colleagues, which include scientists from Bayer, one of the main producers of neonicotinoids, investigated resistance to thiacloprid by looking at bees’ defense systems. The team focused on enzymes known as P450s, which can metabolize toxic chemicals, breaking them down before they affect the bee nervous system. The researchers used drugs to inhibit groups of P450 enzymes. When the family enzymes called CYP9Q was inhibited, bees became 170 times as sensitive to thiacloprid, dying from a much smaller dose, the researchers found. Discovering the enzymes’ protective power could lead to more effective ways to simultaneously avoid harming bees and help crops.
“We live in an era that uses pesticides,” Rundlöf says. “We need to figure out the ones that are safest.”